How does Outlook/Hotmail filtering differ?

Microsoft Outlook.com (including Hotmail and Live) uses SmartScreen technology for filtering. While the principles are similar to other providers, the implementation differs in several ways.

Microsoft operates SNDS (Smart Network Data Services) that provides sender reputation visibility. Unlike Gmail Postmaster Tools, SNDS shows data at the IP level rather than domain level.

The Focused Inbox feature separates mail into Focused and Other tabs based on what Microsoft predicts you want to see. This is distinct from spam filtering.

Microsoft has historically been more aggressive with blocking unknown senders and new IPs. Building reputation with Microsoft often requires more patience than with Gmail.

Sender certification through programs like Return Path (now Validity) has traditionally had more impact at Microsoft than at Gmail.

Each major harbor has its own rules. What works at Gmail may not work identically at Microsoft.